1. Field of the Invention
The present invention relates to a method and an apparatus for constructing images for a three-dimensional surface shading image display obtained from three-dimensional sequential tomographic images collected by an X-ray CT (Computed Tomography) apparatus, NMR (Nuclear Magnetic Resonance) imaging apparatus, or ultrasonic tomography imaging apparatus.
2. Description of the Background Art
In recent years, has become popular to construct a three-dimensional surface shading image display from the three-dimensional voxel data representing the sequential tomographic images obtained by a tomographic imaging apparatus such as an X-ray CT apparatus.
In such a three-dimensional surface shading image display, it is necessary to construct a three-dimensional distance image (referred to hereafter simply as a distance image) as an intermediate data, in order to achieve the three-dimensional image construction. This distance image has conventionally been constructed by the so called ray tracing method which is usually implemented in a form of a computer software, as described by Herman and Liu in "Three-dimensional display of human organs from computed tomograms" Comput Graphics Image Processing 9, pp. 1-21, 1979.
However, such a conventional method of constructing the distance image by using the computer software has been associated with a problem that the processing speed is slow so that a considerable amount of time has been required for the construction of the distance image.
There has also been a proposition for a specialized hardware configuration for realizing the ray tracing method to construct the distance image. However, such a hardware configuration inevitably becomes highly specialized for that purpose alone, so that there has been a drawback that an image construction apparatus adopting such a specialized hardware configuration would have a very poor general applicability.